Localized Changes of Stainless Steel Powder Characteristics During Selective Laser Melting Additive Manufacturing

Galicki, D.; List, F.A.; Babu, S. S.; Plotkowski, Alex; Meyer, H. M.; Seals, Roland D; Hayes, Christopher

doi:10.1007/s11661-018-5072-7

Cited by 30 publications

(19 citation statements)

References 18 publications

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“…A negligible average particle size difference for recycled powders (25 m) versus the virgin powder (26 m) was recorded which is in contrast to Heiden et al as they reported a slightly larger average particle size for reused powder (18.5 m) compared to virgin powder (15.5 m) [15]. Conversely, Galicki et al reported a more irregular shape, slight decrease in particle size but a broader size distribution after 30 recycling steps [27]. They also reported a smaller internal pore volume and surface area for the recycled powders and attributed that to pore collapse under application of the laser heat.…”

Section: X-ray Tomography Analysismentioning

confidence: 77%

“…The volume of the particles from the 3D reconstructed cube did not show much difference between the two powders. There were more smaller particles in the recycled powder compared to its virgin counterpart probably due to the blowing of smaller particles away from the melt pool during processing, as for this a lower level of kinetic energy would be required [27]. Apart from the particle size distribution analysis, extensive testing was carried out using a variety of image processing methods for quantitative pore analysis of the powders [28,29,30].…”

Section: X-ray Tomography Analysismentioning

confidence: 99%

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A new method for assessing the recyclability of powders within Powder Bed Fusion process

Gorji

Saxena

Corfield

et al. 2020

Materials Characterization

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Recycling metallic powders used in the additive manufacturing (AM) process is essential for reducing the process cost, manufacturing time, energy consumption, and metallic waste. In this paper, the focus is on pore formation in recycled powder particles of stainless steel 316L during the selective laser melting process. We have introduced the concept of optimizing the powder bed's printing area in order to see the extent of the affected powders during the 3D-printing process. X-ray Computed Tomography (XCT) is used to characterize the pores inside the particles. The results from image processing of the tomography (rendered in 3D format) indicate a broader pore size distribution and a higher pore density in recycled powders compared to their virgin counterparts. To elucidate on this, the Electron Dispersion spectroscopy (EDX) analysis and Synchrotron-based Hard X-ray Photoelectron Spectroscopy (HAXPES) were performed to reveal the chemical composition distribution across the pore area and bulk of the recycled powder particles. Higher concentrations of Fe, Cr, and Ni were recorded on the interior wall of the pore in recycled particles and higher Mn, S and Si concentrations were recorded in the outer layer around the pore area and on the surface of the recycled particle. The pore formation in recycled powder is attributed to out-diffusion of Mn, S and Si to the outer surface as a result of the incident laser heat during the AM process due to higher electron affinity of such metallic elements to oxygenation. HAXPES analysis shows a higher MnO concentration around the pore area which impedes the in-diffusion of other elements into the bulk and thereby helps to creates a void. The inside wall of the pore area (dendrites), has a higher concentration of Fe and Cr oxide. We believe the higher pore density in recycled powders is due, at least in part to composition redistribution, promoted by laser heat during the AM process. Nanoindentation analyses on both virgin and recycled powder particles shows a lower hardness and higher effective modulus in the recycled powder particles attributed to the higher porosity in recycled powders.

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Section: X-ray Tomography Analysismentioning

confidence: 77%

Section: X-ray Tomography Analysismentioning

confidence: 99%

A new method for assessing the recyclability of powders within Powder Bed Fusion process

Gorji

Saxena

Corfield

et al. 2020

Materials Characterization

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“…What is most striking from the results performed on many different alloys (stainless steels, Ti-6Al-4V, Alsi10Mg, IN718 and IN625, Co-Cr, Scalmalloy) [19,30,37,58,[82][83][84][85][86][87][88], in terms of reused powder characterization and, most importantly, of the microstructural and mechanical properties of the final parts, is that, while the former are quite similar for the same alloy, the latter are characterized by very scattered results [23]. Mechanical properties could be improved, decreased, or unaffected by the reuse of feedstock material, as shown by the results reported in Table 1.…”

Section: Powder Feedstock Featuresmentioning

confidence: 99%

Material Reuse in Laser Powder Bed Fusion: Side Effects of the Laser—Metal Powder Interaction

Santecchia

Spigarelli

Cabibbo

2020

Metals

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Metal additive manufacturing is changing the way in which engineers and designers model the production of three-dimensional (3D) objects, with rapid growth seen in recent years. Laser powder bed fusion (LPBF) is the most used metal additive manufacturing technique, and it is based on the efficient interaction between a high-energy laser and a metal powder feedstock. To make LPBF more cost-efficient and environmentally friendly, it is of paramount importance to recycle (reuse) the unfused powder from a build job. However, since the laser-powder interaction involves complex physics phenomena and generates by-products which might affect the integrity of the feedstock and the final build part, a better understanding of the overall process should be attained. The present review paper is focused on the clarification of the interaction between laser and metal powder, with a strong focus on its side effects. Figure 1. Schematics of the laser powder bed fusion (LPBF) equipment. Adapted from Reference [9] with permission from Elsevier.While the market and the applications of laser powder bed fusion continuously and impressively grew in recent years, there is a common view across users and researchers concerning the repeatability of the process in terms of chemical composition and mechanical properties of the final parts, which are of paramount importance when challenging environmental or testing conditions are considered [10][11][12][13][14][15][16].The most typical approach to study the microstructural and mechanical properties of parts built by LPBF is to compare them with castings of the same alloy or, rather, the corresponding alloy since the starting material is metal powder rather than a fuse. However, in some existing alloys designed for cast and wrought parts, laser additive manufacturing processing results in cracking or other microstructure deficiencies [11,12,16,17]. It is worth noting that LPBF has more similarities with laser welding rather than casting, since the two laser-based techniques have some common features (i.e., melt-pool formation, moving heat source) [18]. However, process parameters are, in general, quite different in terms of laser power and scan speed, and the laser-matter interaction is much more complicated in LPBF processes, since the powder feedstock is inherently unstable and the solidified material undergoes multiple thermal cycles corresponding to the fusion of subsequent layers during the additive process [19][20][21][22]. Furthermore, owing to the similarities with welding and to the complicated interaction between laser and metal particles, when comparing laser powder bed fusion with other metal forming processes, it is evident that the range of processable alloys is very limited and the number of high-productivity commercially available alloys is even smaller [23]. One of the reasons behind this is that the level of metal powder sensitivity to the laser action during LPBF is not yet fully understood, despite the efforts of the scientific community to uncover it [24][25][26][27], and ...

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“…However, the recycling of used powders may induce alterations in their physical properties and chemistry, which could affect the eventual mechanical properties of the as-built parts [27]. In fact, studies have shown that the recycled powders will almost always have larger particle sizes, rougher surface areas, reduced particle circularity, increased contamination, and a higher uptake of oxygen, nitrogen, or other inert gases regardless of the number of reuse times [53][54][55][56][57][58][59][60][61].…”

Section: Introductionmentioning

confidence: 99%

Comparison between Virgin and Recycled 316L SS and AlSi10Mg Powders Used for Laser Powder Bed Fusion Additive Manufacturing

Yusuf

Choo

Gao

2020

Metals

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In this study, the comparison of properties between fresh (virgin) and used (recycled) 316L stainless steel (316L SS) and AlSi10Mg powders for the laser powder bed fusion additive manufacturing (L-PBF AM) process has been investigated in detail. Scanning electron microscopy (SEM), electron-dispersive X-ray spectroscopy (EDX), and X-ray diffraction (XRD) techniques are used to determine and evaluate the evolution of morphology, particle size distribution (PSD), circularity, chemical composition, and phase (crystal structure) in the virgin and recycled powders of both materials. The results indicate that both recycled powders increase the average particle sizes and shift the PSD to higher values, compared with their virgin powders. The recycled 316L SS powder particles largely retain their spherical and near-spherical morphologies, whereas more irregularly shaped morphologies are observed for the recycled AlSi10Mg counterpart. The average circularity of recycled 316L SS powder only reduces by ~2%, but decreases ~17% for the recycled AlSi10Mg powder. EDX analysis confirms that both recycled powders retain their alloy-specific chemical compositions, but with increased oxygen content. XRD spectra peak analysis suggests that there are no phase change and no presence of any undesired precipitates in both recycled powders. Based on qualitative comparative analysis between the current results and from various available literature, the reuse of both recycled powders is acceptable up to 30 times, but re-evaluation through physical and chemical characterizations of the powders is advised, if they are to be subjected for further reuse.

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Localized Changes of Stainless Steel Powder Characteristics During Selective Laser Melting Additive Manufacturing

Cited by 30 publications

References 18 publications

A new method for assessing the recyclability of powders within Powder Bed Fusion process

A new method for assessing the recyclability of powders within Powder Bed Fusion process

Material Reuse in Laser Powder Bed Fusion: Side Effects of the Laser—Metal Powder Interaction

Comparison between Virgin and Recycled 316L SS and AlSi10Mg Powders Used for Laser Powder Bed Fusion Additive Manufacturing

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